Display apparatuses which include active matrix substrates in which respective switching elements are installed for respective pixels are broadly used. The active matrix substrates including thin film transistors (hereinafter referred to as “TFTs”) as the switching elements are referred to as TFT substrates. In the present specification, portions of the TFT substrates corresponding to pixels of the display apparatuses are referred to as pixels in some cases.
In recent years, oxide semiconductors are proposed to be used as materials of active layers of TFTs, instead of amorphous silicon or polycrystal silicon. The TFTs are referred to as “oxide semiconductor TFTs”. The oxide semiconductors have mobility higher than the amorphous silicon. Therefore, the oxide semiconductor TFTs can operate at a higher speed than the amorphous silicon TFTs. Since oxide semiconductor films are formed in simpler processes than polycrystal silicon films, the oxide semiconductor films can also be applied to apparatuses which may have large areas.
A TFT substrate in which oxide semiconductor TFTs are used is disclosed in, for example, PTL 1. In the TFT substrate disclosed in PTL 1, an oxide semiconductor TFT (hereinafter simply abbreviated for a “TFT”) held by a substrate and a pixel electrode electrically connected to a drain electrode of the TFT are included for each pixel. The TFT is normally covered with an inter-layer insulation layer. A pixel electrode is installed on the inter-layer insulation layer and is connected to a drain electrode of the TFT in a contact hole formed in the inter-layer insulation layer. Such a structure is disclosed in, for example, PTL 1. In the present specification, a connection portion between the drain electrode and the pixel electrode of the TFT is referred to as a “contact portion”. A region opened by the contact hole, that is, a region which is the bottom surface of the contact hole, is referred to as an “opening region of the contact hole” in some cases.
In the contract portion disclosed in PTL 1, the drain electrode has a larger pattern than the bottom surface (opening region) of the contact hole installed in an inter-layer insulation layer in consideration of an alignment error or the like in a manufacturing process when viewed in the normal direction of a substrate. Thus, since the entire opening region of the contact hole is disposed to overlap the drain electrode, it is possible to ensure a contact area of the drain electrode and the pixel electrode. The entire contact portion can be shielded from light by the drain electrode.